The present invention relates to a photothermographic material. In particular, the present invention relates to a novel photothermographic material that enables control of image color tone and reduction of silver amount to be used by forming dye images by heat development.
Methods for forming images by heat development are described in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Klosterboer, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d, Imaging Processes and Materials, Neblette, 8th ed., compiled by J. Sturge, V. Walworthand A. Shepp, Chapter 9, p.279, (1989). Such photothermographic materials comprise a reducible non-photosensitive silver source (e.g., silver salt of an organic acid), a photocatalyst (e.g., silver halide) in a catalytically active amount and a reducing agent for silver, which are usually dispersed in an organic binder matrix. While the photosensitive materials are stable at an ordinary temperature, when they are heated to a high temperature (e.g., 80xc2x0 C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image generated upon exposure. The silver produced from the reaction of the reducible silver salt in the exposed areas shows black color and provides contrast with respect to the non-exposed areas, and thus images are formed.
A method of releasing or forming diffusible dyes imagewise by heat development and transferring these diffusible dyes to an image-receiving material was proposed. In this method, either of a negative dye image and a positive dye image can be obtained by changing the kind of dye-donating compound or the kind of silver halide to be used. Further details are disclosed in U.S. Pat. Nos. 4,500,626, 4,483,914, 4,503,137, 4,559,290, Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 58-149046, JP-A-60-133449, JP-A-59-218443, JP-A-61-238056, EP220746A2, JIII Journal of Technical Disclosure (Kokai Giho) No. 87-6199 and EP210660A2 and so forth.
Various methods have been proposed as for methods of obtaining positive color images by heat development. For example, U.S. Pat. No. 4,559,290 discloses a method in which a so-called dye releasing redox compound (hereinafter also referred to as a DRR compound) converted into a compound of oxidized form having no dye-releasing ability is used together with a reducing agent or a precursor thereof, so that the reducing agent should be oxidized in proportion to the exposure amount of silver halide by heat development, and the compound is reduced with the remaining reducing agent not oxidized so that the compound should release diffusible dyes. Further, EP220746A and JIII Journal of Technical Disclosure (Kokai Giho) No. 87-6199 (vol. 12, No. 22,) disclose color photothermographic materials using, as a compound that releases diffusible dyes by a similar mechanism, a compound which releases diffusible dyes by reductive cleavage of N-X bond (X represents an oxygen atom, a nitrogen atom or a sulfur atom).
As a method for forming dye images for photographic materials, the method utilizing a coupling reaction of a coupler and an oxidation product of developing agent is most commonly used, and color photothermographic materials utilizing this method are described in U.S. Pat. Nos. 3,761,270, 4,021,240, JP-A-59-231539, JP-A-60-128438 and so forth. In the techniques disclosed in the aforementioned patent documents, p-sulfonamidophenol is used as a developing agent. Because, in the photosensitive materials of coupling type, the couplers do not show absorption in the visible region before development, they are more advantageous in view of sensitivity compared with the photosensitive materials utilizing the aforementioned color materials, and they are considered to have an advantage that they can be used not only as printing materials but also as image-capturing materials.
These methods for obtaining dye images by heat development are suitable for photothermographic materials utilizing thermal transfer, diffusion transfer or sublimation type thermal transfer from a photosensitive layer to an image-receiving layer. However, for obtaining dye images as photothermographic materials of monosheet type, they do not necessarily have suitable characteristics as for image-forming temperature, image stability and color tone.
In photothermographic materials, compounds called xe2x80x9ctoning agentsxe2x80x9d are added to the photosensitive materials as required, in order to improve image density of silver images, silver color tone, and heat developability.
In photothermographic materials utilizing silver salts of an organic acid, toning agents of a wide range can be used. Examples of the toning agent are disclosed in, for example, JP-A-46-6077, JP-A-47-10282, JP-A-49-5019, JP-A-49-5020, JP-A-49-91215, JP-A-50-2524, JP-A-50-32927, JP-A-50-67132, JP-A-50-67641, JP-A-50-114217, JP-A-51-3223, JP-A-51-27923, JP-A-52-14788, JP-A-52-99813, JP-A-53-1020, JP-A-53-76020, JP-A-54-156524, JP-A-54-156525, JP-A-61-183642, JP-A-4-56848, Japanese Patent Publication (Kokoku, hereinafter referred to as JP-B) 49-10727, JP-B-54-20333, U.S. Pat. Nos. 3,080,254, 3,446,648, 3,782,941, 4,123,282 and 4,510,236, British Patent No. 1,380,795, Belgian Patent No. 841,910, JP-B-1-25050 and so forth.
Specific examples of the toning agent include phthalimide and N-hydroxyphthalimide; succinimide, and cyclic imides such as pyrazolin-5-ones, quinazolinone, 3-phenyl-2-pyrazolin-5-one, 1-phenylurazole, quinazoline and 2,4-thiazolidinedione; naphthalimides such as N-hydroxy-1,8-naphthalimide; cobalt complexes such as cobalt hexaminetrifluoroacetate; mercaptanes such as 3-mercapto-1,2,4-triazole, 2,4-dimercaptopyrimidine, 3-mercapto-4,5-diphenyl-1,2,4-triazole and 2,5-dimercapto-1,3,4-thiadiazole; N-(aminomethyl)aryldicarboxyimides such as N,N-(dimethylaminomethyl)phthalimide and N,N-(dimethylaminomethyl)naphthalene-2,3-dicarboxyimide; blocked pyrazoles, isothiuronium derivatives and a certain kind of photobleaching agents such as N,Nxe2x80x2-hexamethylenebis(1-carbamoyl-3,5-dimethylpyrazole), 1,8-(3,6-diazaoctane)bis(isothiuroniumtrifluoroacetate, and 2-(tribromomethylsulfonyl)benzothiazole; 3-ethyl-5-[(3-ethyl-2-benzothiazolinylidene)-1-methylethyli dene]-2-thio-2,4-oxazolidinedione; phthalazinone, phthalazinone derivatives and metal salts thereof such as 4-(1-naphthyl)phthalazinone, 6-chlorophthalazinone, 5,7-dimethyloxyphthalazinone or 2,3-dihydro-1,4-phthalazinedione; combinations of phthalazinone with a phthalic acid derivative such as phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, tetrachlorophthalic acid anhydride and homophthalic acid; phthalazine, phthalazine derivatives such as 4-(1-naphthyl)-phthalazine, 6-chlorophthalazine, 5,7-dimethoxyphthalazine, 6-isopropylphthalazine, 6-isobutylphthalazine, 6-tert-butylphthalazine, 5,7-dimethylphthalazine and 2,3-dihydrophthalazine, and metal salts thereof; combinations of phthalazine or a derivative thereof and a phthalic acid derivative such as phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, tetrachlorophthalic acid anhydride and homophthalic acid; quinazolinedione, benzoxazine and naphthoxazine derivatives; rhodium complexes that function not only as a toning agent but also as a halide ion source for the formation of silver halide at the site, such as ammonium hexachlororhodate(III), rhodium bromide, rhodium nitrate and potassium hexachlororhodate (III); inorganic peroxides and persulfates such as ammonium disulfide peroxide and hydrogen peroxide; benzoxazine-2,4-diones such as 1,3-benzoxazine-2,4-dione, 8-methyl-1,3-benzoxazine-2,4-dione and 6-nitro-1,3-benzoxazine-2,4-dione; pyrimidines and asymmetric triazines such as 2,4-dihydroxpyrimidine and 2-hydroxy-4-aminopyrimidine; azauracil and tetraazapentalene derivatives such as 3,6-dimercapto-1,4-diphenyl-1H,4H-2,3a,5, 6a-tetraazapentalene and 1,4-di(o-chlorophenyl)-3,6-dimercapto-1H, 4H-2,3a,5,6a-tetraazapentalene and so forth.
These toning agents have been searched in view of desired performances (image density, silver color tone, improvement of heat developability), properties of volatilization, sublimation or the like from photosensitive materials, properties of photosensitive materials comprising them in combination with other additives such as antifoggants and so forth, and many toning agents have been reported. It is known that, among those, superior results can be obtained by combinations of phthalazine compounds and phthalic acid derivatives. However, if these toning agents are used in order to control color tone of photosensitive materials in a specific wavelength region, the relationship between types and structures of toning agents and obtainable silver color tone may readily be fluctuated by various factors including combination with other additives, production conditions of photosensitive materials, development temperature, lapse of time and so forth, and it has constituted an important problem in designing of photothermographic materials. Therefore, there has been desired a photothermographic material that can solve this problem.
An object of the present invention is to solve the aforementioned problems of the prior art. That is, the object to be achieved by the present invention is to provide a novel photothermographic material that shows good photographic properties including sensitivity, fog and so forth, and enables control of color tone of the photothermographic material in an arbitrary wavelength region by realizing efficient color formation reaction even as a monosheet type photothermographic material.
The inventors of the present invention assiduously studied in order to achieve the aforementioned object. As a result, they found that a photothermographic material exhibiting superior color formation effect could be obtained by using a reducing compound having a particular structure, a coupler compound and a phthalic acid compound having a particular structure, and thus accomplished the present invention.
That is, the present invention provides a photothermographic material comprising (a) a photosensitive silver halide, (b) a reducible silver salt, (c) a reducing compound represented by the following formula (1) or (2), (d) a binder, (e) a coupler compound, and (f) a compound represented by the following formula (3), on a side of a support. 
In the formula (1), V1 to V4 each independently represent hydrogen atom or a substituent, and V5 represents a substituted or unsubstituted alkyl group, aryl group or heterocyclic group.
Q1xe2x80x94NHNHxe2x80x94V6xe2x80x83xe2x80x83(2)
In the formula (2), Q1 represents a 5- to 7-membered unsaturated ring bonding to NHNHxe2x80x94V6 at a carbon atom, and V6 represents a carbamoyl group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a sulfonyl group or a sulfamoyl group. 
In the formula (3), P represents a monovalent substituent, m represents an integer of 1-4, and M represents hydrogen atom or a counter ion.
Preferably, the reducing compound is a reducing compound represented by the formula (2).
Preferably, the photothermographic material of the present invention further contains (g) an organic polyhalogenated compound represented by the formula (4) on the image-forming side of the support.
Q2"Parenopenst"(Y)"Parenclosest"nCZ1Z2Xxe2x80x83xe2x80x83(4)
In the formula (4), Q2 represents an alkyl group, aryl group or heterocyclic group, which may have one or more substituents, Y represents a divalent bridging group, n represents 0 or 1, Z1 and Z2 each independently represent a halogen atom, and X represents hydrogen atom or an electron-withdrawing group.
Preferably, the coupler compound is a compound represented by any one of the following formulas (5) to (19): 
In the formulas (5) to (19) X1 to X15 each independently represent hydrogen atom or a substituent. In the formula (5), R1 and R2 each independently represent an electron-withdrawing group. In the formulas (6) to (19), R3 to R28 each independently represent hydrogen atom or a substituent. In the formula (16), q represents an integer of 0-4. In the formulas (18) and (19), n1 and n3 each independently represent an integer of 0-4, and n2 represents an integer of 0-2.
Preferably, the photothermographic material of the present invention further contains (h) a compound represented by the formula (20) or (21) on the image-forming side of the support. 
In the formula (20), V7 to V14 each independently represent hydrogen atom or a substituent. L represents a bridging group consisting of xe2x80x94CH(V15)xe2x80x94 or xe2x80x94Sxe2x80x94. V15 represents hydrogen atom or a substituent. 
In the formula (21), V1 to V20 each independently represent hydrogen atom or a substituent.
Preferably, the photothermographic material of the present invention is a monosheet type photosensitive material.
According to another aspect of the present invention, there is provided a method for forming images, which comprises developing the aforementioned photothermographic material of the present invention by heating.
According to the present invention, there can be obtained a novel photothermographic material that shows good photographic properties including sensitivity, fog and so forth, and enables control of color tone of the photothermographic material so that it should have absorption at an arbitrary wavelength region by realizing efficient color formation reaction.